Methods of capturing tomographic images taking a living body as a measurement object include X-ray computerized tomography (CT) using X-rays, ultrasound CT using ultrasound, NMR-CT using nuclear magnetic resonance, and proton CT using a particle beam of protons or the like.
Meanwhile, optical tomography (called optical CT below) can be applied to the tomographic observation of small animals because living body tissue transmits light of predetermined wavelengths such as near-infrared light.
When a living body is irradiated with light, the light passes through the living body while scattering isotropically; thereby, light corresponding to the light with which the living body has been irradiated is emitted from around the living body. Based on this, in optical CT, a living body that is a measurement object is irradiated with light of a predetermined wavelength, and the intensity of the light transmitted through the measurement object and radiating around it is detected. Further, in optical CT, by changing the positions of irradiation with the light and receiving the emitted light, measurement information that is the basis of tomographic information (optical tomographic information) of the measurement object can be acquired.
Within a living body or the like, in contrast to within air and so forth in which the straightness of light can be ensured, light scattering and absorption occur. For this reason, in order to obtain adequate tomographic information of a living body, it is necessary to adequately grasp the outer shape of the measurement object.
For example, Non-Patent Document 1 proposed three-dimensionally measuring of the shape of a measurement object beforehand, and Patent Document 1 proposes filling a container with a solution whose optical properties, such as its absorption coefficient and its scattering coefficient with respect to light, substantially coincide with those of the measurement object, immersing the measurement object in this solution, and acquiring tomographic information including the container.    Non-patent Document 1: IEEE Transaction on Medical Imaging, Vol. 23, No. 4, April 2004    Patent Document 1: JP-A No. 11-173976